This invention relates to release mechanisms for power tool bits. More particular, it relates to an improved mechanism for connecting and disconnecting bits from rotary power tools, such as air or electrically powered screwdrivers and nut setters, and for exchanging the entire bit holding mechanism of rotary power tools.
Rotary power tools, including air powered or electrically driven screwdrivers and nut setters, have long been used in industrial assembly operations. Such rotary tools have been produced in many varieties. They are typified by the disclosures in such patents as DePagter, U.S. Pat. No. 4,078,618 issued Mar. 14, 1978 for a "Torque Controller Shutoff Mechanism"; Wallace, U.S. Pat. No. 4,071,092 issued Jan. 31, 1978 for a "Pneumatic Screwdriver with Torque Response Shut-Off"; Dudek, U.S. Pat. No. 3,734,515 issued May 22, 1973 for a "Power Wrench with Interchangeable Adapters"; Sorensen, U.S. Pat. No. 3,129,642 issued Apr. 21, 1964 for a "Pneumatically Operated Tool"; and British Pat. No. 1,117,583 issued June 19, 1968 for "Improvements in or relating to Fluid Operated Tools". Such rotary power tools for industrial applications usually consist of a motor or other drive mechanism (frequently powered by a high pressure air source), a bit driven by the drive mechanism, a clutch mechanism to engage the drive, and a release mechanism to allow the exchange of different sizes and kinds of bits. This invention is directed to an improved form of a release mechanism.
Many different release mechanisms have been developed in the prior art. Each allows bits to be quickly exchanged so that different bits may be easily used by the same tool in the same assembly operation. Such bit release mechanisms conventionally employ a ball cooperating with an annular groove that is machined in the shaft of the bit. The ball usually cooperates with a sleeve mounted outside of the power tool's housing. The sleeve typically has an internal ring or similar structure that forces the ball into the annular groove of the bit, thereby preventing the bit from being released from the tool. The ball may normally be moved away from the bit's groove by sliding the sleeve along the exterior of the tool's housing. The sleeve's movement removes the ring from vicinity of the ball and allows the bit to slide from the tool without hinderance from the ball. Such tools conventionally use an internal coil spring to hold the sleeve ring in position over the ball. The spring and sleeve then retain the ball in the bit's annular groove, and the bit is then held within the tool during normal tool use.
An example of the above described conventional release mechanism is disclosed in DePagter, U.S. Pat. No. 4,078,618. In such mechanisms, the shafts of the bits are all constructed in standard size and configuration (usually with a hexagonal cross section at the bit's lower end) so that a variety of different bit sizes and types may be inserted within a single tool.
While the conventional power screwdrivers and nut setters described above allow relatively easy exchange of bits, they often encounter greater difficulty in adapting the tool for use with substantially different kinds of bits, especially bits having attachments. For example, rotary powered tools are often used with an attachment called a "finder" (either magnetic or nonmagnetic) that is mounted on the tool around the bit. Finders are well known to perhaps of skill in the art, and allow quick placement of the bit on a screw or nut, and consequent faster assembly operations.
In instances where attachments such as finders are used, conventional bit retainer mechanisms may be inadequate, since conventional mechanisms often do not easily allow different sizes or shapes of finders to be inserted into the retention retainer mechanism. In other circumstances, attachments of an entirely different sort are desired to be placed on the end of a power tool, so that complete replacement of the retention mechanism may be desirable. Conventional bit retainers with external retention sleeves usually do not lend themselves to an easy exchange of mechanisms. If an assembly operation requires different attachments, several different models of tool must be used, each corresponding to a particular kind of bit or attachment. Likewise, tool manufactures must develop several different models of tools to hold the different attachments.
One solution to the problem is disclosed by Sheldon, U.S. Pat. No. 4,209,182 issued June 24, 1980 for a "Bit Retainer for Screwdriver". The Sheldon patent discloses a bit release mechanism having a removable internal sleeve. The sleeve cooperates with a ball in the conventional fashion to allow removal of a bit. However, because the internal sleeve is removable, different sleeves adapted to hold different release mechanisms corresponding to different attachments can be placed in the tool when desired. Additionally, the internal sleeve arrangement allows mechanism such as finders to extend around the bit and into the interior of the sleeve, if necessary.
The Sheldon mechanism, unlike conventional release mechanisms, does not use a spring-biased sleeve. Instead, it uses an unbiased sleeve that is positioned in the tool housing by a camming action between a pin held by a leaf spring and shoulders that are machined into the external surface of the sleeve. Although the Sheldon mechanism is effective in allowing both the exchange of bits and the removal and interchange of sleeves, that mechanism still is not ideal, because substantial difficulties can arise in securing the unbiased sleeve within the tool. For example, frequent operation of the mechanism, or frequent removal of the pin, can reduce the pressure exerted by the leaf spring on the pin, thereby making the mechanism less capable of retaining the sleeve in the tool. An improved mechanism allowing the advantages of the Sheldon patent but preventing its disadvantages is therefore desirable.